Continuous Positive Airway Pressure (CPAP) is one of the most effective treatments for sleep apnea syndrome. This treatment utilizes respiratory equipment providing a positive pressure gas in the range of 400 to 2000 Pa in the nostrils, or the nostrils and the mouth, or the face of a user during sleep. Further, Nasal Intermittent Positive Pressure Ventilation (NIPPV) is one of the most effective treatments for ventilatory insufficiency, utilizing respiratory equipment providing an intermittent positive pressure gas in the range of 400 to 2400 Pa in the nostrils of a user.
As respiratory used in these therapies, there are nasal masks providing a positive pressure gas in the nostrils under pressure, full-face masks providing the positive pressure gas holding the nostrils and the mouth, and total face masks providing the positive pressure gas over the entire face.
These respiratory masks are secure to the head of a user by a strap portion connected to a head mount of a headgear worn in the proximity of the opistocranion of the head of the user (JIS Z8500, ISO 7250).
When performing treatment using the above stated equipment, in order to provide a continuous positive pressure gas to the nostrils and the like of a user generally, the respiratory mask is comprised of an elbow connecting a hose guiding the positive pressure gas for respiration, a frame connecting with the elbow to hold a mask cushion in a specified position, and a hollow mask cushion which is closely attached to the face of a user. Such a respiratory mask is closely attached to the face of a user by the tension of the stretchable strap portion of the headgear (for example, see Japanese Patent Kokai No. 11-000397; Pamphlet of International Publication No. WO01/097893, and Pamphlet of International Publication No. 98/04310).
However, once, the respiratory mask is normally installed, it is known that displacement of the mask cushion occurs due to various causes while wearing. Because of that, measures have been taken which prevent or reduce the displacement corresponding to the respective causes. For example, to this end, a bellows is provided between the frame portion and the face contact portion of the mask cushion, in the nasal respiratory masks described in Japanese Patent Kokai No. 11-000397 and Pamphlet of International Publication No. WO 01/097893 to prevent an influence on the mask cushion from the displacement of the frame portion which occurs by contact with bed clothing. Further, in a respiratory mask described in Pamphlet of International Publication No. WO 96/17643, a flexible material is used for the wall around the connection portion of the positive pressure gas supply hose in order to reduce the displacement of the frame portion caused when it is pulled by the positive pressure gas supply hose connected to the frame.
Such a displacement causes the supplied positive pressure gas to leak, from the boundary between the mask cushion and the face, giving discomfort, irritation to the ocular region, and chills and the like to the user due to gas leaks, and depending on the case treatment is obliged to be discontinued. The gas leakage from the mask cushion in such conventional technology remarkably takes place in the root of nose region, nasal alae region and the like. For preventing such gas leaks, there is but one method which further strongly tightens the belt for securing a respiratory mask regardless of the location of the leak, but it is indicated that when wearing all night long for a long period of time during sleep and the like, it is possible that a respiratory mask can harm the face of a user.